1. Field of the Invention
The present invention relates to transversal filters employing charge transfer technology, and more particularly to a programmable or adaptable charge coupled device or bucket brigade device transversal filter employing temporary charge summation on field effect transistor gates in combination with charge transfer shift registers to perform analog signal processing.
2. Description of the Prior Art
Transversal filters having adjustable weighting factors and including bucket brigade charge transfer shift registers are known. One example is described in U.S. Pat. No. 3,809,923 issued May 7, 1974 to Esser on an application filed Jan. 29, 1973 and assigned to U.S. Philips Corporation. This patent is directed to a transversal filter employing charge transfer wherein the problem of charge leakage through resistors associated with the coupled storage capacitors is avoided by charging the storage capacitors through weighted current dividers. The patent does not teach or show a transversal filter of the present invention where the charges can be replicated or temporarily added on the gates of individual FETs and also does not provide for a register system wherein the input signal and the reference signal can both be translated.
In the publication entitled "An Electrically Programmable LSI Transversal Filter for Discrete Analog Signal Processing (DASP)", by D. R. Lampe, M. H. White, J. H. Mims and J. L. Fagan, Report ECOM Contr. No. DAAB07-73-C-0337, Westinghouse Electric Corporation, Defense and Electronic Systems Center, Systems Development Division, Baltimore, Md. 21203, a combination CCD and programmable MNOS memory bank is described which performs the operations of translation, multiplication and summing to provide an adaptable transfer function device. However, the filter transfer function of this reference is not directly controlled by one of the analog signals, instead the tap values are electronically trimmed using MNOS conductances. A further distinction is that the CCD and the MNOS memory are not equivalent structures as in the present invention.
Other references of background interest are "Bucket Brigade Transversal Filters", C. M. Puckette et al., IEEE Transactions of Circuits and Systems, Vol. CAS-21, No. 4July 1974, p. 502; "Programmable Bandpass Filter and Tone Generator Using Bucket Brigade Delay Lines ", D. A. Smith et al, IEEE Transactions on Circuits and Systems, Vol. CAS-21, No. 4 July 1974, p. 597; "Transversal Filtering Using Charge-Transfer Devices" by D. D. Buss et al., IEEE J. Solid-State Circuits, Vol. SC-8, No. 2 April 1973, p. 138; and U.S. Pat. No. 3,819,958 issued June 25, 1974 to Gosney on an application filed Nov. 3, 1972 entitled "Charge Transfer Device Analog Matched Filter" and assigned to Texas Instruments, Inc.; "Analogue Correlators Using Charge Coupled Devices", J. G. Harp et al., Int. Conf. on the Appl. of CCDs, NELC - San Diego, 1975, pp. 229-235.